An investigation by a French investigative journalist has reported that eighty percent of Vatican priests "are secretly gay," according to the study's findings.

The investigation was carried out Frederic Martel, who says that some gay priests are not active, but still, have secret relationships – or have casual sex, often with male prostitutes - including some of the Catholic Church's fiercest critics of homosexuality.

Martel probed the sexuality of Catholic clergy for his new book, "In the Closet of the Vatican," for which he spent four years in the Vatican and conducted 1500 interviews and interviewed 200 Catholic priests.

Martel claims that his study found that the more homophobic and conservative the priest, the "more likely" they are to be gay.

Martel based his book on vast number interviews he conducted, which also included other Vatican officials, during the 200 weeks he spent in the holy city.

Although the book does not conflate homosexuality with the sexual abuse of children, Martel describes a secretive culture among priests that creates conditions in which abuse is not confronted.

According to Metro, Martel claims that the late Colombian cardinal Alfonso López Trujillo, a staunch defender of the Church’s conservative views on homosexuality, was secretly gay and used male prostitutes.

Martel spent 200 weeks in residences inside the Vatican, according to The Tablet.

He interviewed more than 200 priests, 41 cardinals and 52 bishops and monsignors.

Publisher Bloomsbury describes the book as a "startling account of corruption and hypocrisy at the heart of the Vatican."